From: "H. Peter Anvin" <hpa@zytor.com>
To: Vegard Nossum <vegard.nossum@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Optimize is_power_of_2().
Date: Fri, 15 Jun 2007 11:21:17 -0700 [thread overview]
Message-ID: <4672D89D.7010801@zytor.com> (raw)
In-Reply-To: <1181926602.25193.5.camel@grianne>
Vegard Nossum wrote:
> From: Vegard Nossum <vegard@peltkore.net>
> Date: Fri, 15 Jun 2007 18:35:49 +0200
> Subject: [PATCH] Optimize is_power_of_2().
>
> Rationale: Removes one conditional branch and reduces icache footprint.
> Proof: If n is false, the product of n and any value is false. If n is
> true, the truth of (n * x) is the truth of x.
>
You realize that on a lot of platforms, multiplication is done by an
out-of-line subroutine, and that even on those that aren't, it's
generally a long-pipeline operation, right?
-hpa
next prev parent reply other threads:[~2007-06-15 18:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-15 16:56 [PATCH] Optimize is_power_of_2() Vegard Nossum
2007-06-15 18:21 ` H. Peter Anvin [this message]
2007-06-15 18:28 ` Robert P. J. Day
2007-06-15 20:26 ` H. Peter Anvin
2007-06-15 19:47 ` Jan Engelhardt
2007-06-15 19:54 ` David M. Lloyd
2007-06-15 19:57 ` David M. Lloyd
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